فناوری، تجارت، و نابرابری دستمزدها در مکزیک قبل و بعد از پیمان نفتا

Over the past few years, there has been a substantial increase in wage inequality between skilled and unskilled workers in Mexico. This increment in the wage gap coincided with both a period of rapid technological change and the process of trade liberalization in Mexico that began in the mid-1980s. Using a methodology suggested by Leamer [Leamer, E., 1998. In search of Stolper–Samuelson linkages between international trade and lower wages. In: Susan Collins (Ed.), Imports, Exports and the American Worker, Brookings Institution, pp. 141–202], we separate out the effects of technological progress and trade on the real wage evolution of skilled and unskilled workers in Mexico's manufacturing industry for the periods 1988–1994 and 1994–2000. We find that, as implied by the Stolper–Samuelson theorem, trade liberalization would have led to a reduction in the wage gap in Mexico in the first period. This effect, however, was offset by the large negative impact of technological progress on the real wage of unskilled workers. On the other hand, during the period 1994–2000 the effect of trade liberalization on the wage gap was nil, thus suggesting that the slight increase in wage inequality that occurred in this period was also driven by technological progress.

Over the past two decades, there has been a continuous increase in the wage gap between skilled and unskilled workers in several developed and developing countries OECD, 1997, Gottschalk and Smeeding, 1997 and Wood, 1997. In many developed countries, but particularly in the case of the United States, there has been a heated debate about the underlying causes of such a trend. There have been two main lines of argumentation: first, higher volumes of trade with emerging or low-income countries may have led, through the mechanisms described by the Hecksher–Ohlin model and the Stolper–Samuelson theorem, to a reduction in the relative price of the less-abundant factor in rich countries (namely, unskilled labor).1 The intuition is that by increasing trade with unskilled labor-abundant countries, the domestic relative price of products intensive on the developed countries' abundant factor (skilled labor) will rise, and this in turn will be associated to an increase in the relative wages of the abundant factor. The second line of argumentation suggests that there has been a worldwide skill-biased technological change that has increased the demand for skilled workers relative to that of unskilled workers Bhagwati, 1995 and Krugman and Lawrence, 1993. Some of the authors that favor this explanation for the US case, rule out the possibility that trade could have been the main explanatory factor of the increase in US wage inequality on the basis that US trade with developing countries is relatively small. Since both arguments are theoretically compelling, a definitive answer about the sources of wage inequality in developed countries was expected to come from empirical studies. However, empirical works based on the US experience provided mixed or weak evidence and therefore did not contribute to resolve the debate.2 In light of these results, some authors suggested to look at the experience of developing countries (i.e. Hanson and Harrison, 1999). They reasoned that, if trade was behind the relative wage movements in developed countries, we should observe a movement in the opposite direction in the relative wages of developing countries. That is, if trade with developing countries was increasing the wage gap between skilled and unskilled workers in developed countries, we should observe a corresponding reduction in the wage gap in the former countries. However, if skill-biased technological change was the main force behind the relative wage movements in developed countries, a similar pattern should be present in developing countries too. Based on this premise, a number of authors have since then analyzed the relationship between wage inequality and trade in developing countries.3 The initial empirical evidence was apparently unequivocal: most developing countries that had gone through episodes of trade liberalization had also experienced a substantial increase in wage inequality Robbins, 1996a and Robbins, 1996b. This result led some authors to conclude that skill-biased technological change was pervasive around the world and that it was the main source of wage inequality in both developed and developing countries (i.e. Berman et al., 1998).4 However, proponents of the trade hypothesis quickly noted that the fact that middle-income countries were experiencing an increase in wage inequality was not necessarily incompatible with their arguments. These authors emphasized that a country could be at the same time abundant in unskilled labor at a local level, but abundant in skilled labor at a global level (Leamer, 1996).5 Therefore, when poor and highly populated countries such as India and China opened their economies to the rest of the world, as they did it in the 1980s, the supply of unskilled labor increased at a worldwide level, and this could explain the pattern of wage inequality observed in middle-income countries (Wood, 1997). This new interpretation complicated again the identification of the role that trade and technology were playing in explaining the increase in wage inequality, since both aspects would be acting in the same direction in both developed and developing countries. In that sense, the resolution to this debate critically depends now on the identification of the contribution of both aspects to the observed pattern of wage inequality. This paper analyzes the role of technological change and trade liberalization in Mexico's wage inequality between 1988 and 2000. For several reasons, the Mexican case seems appropriate to shed light on the debate of trade versus technology as possible sources of wage inequality. First, Mexico unilaterally reduced its tariff and non-tariff barriers during the mid-1980s and has signed several free trade agreements since the beginning of the 1990s. This means that the Mexican economy is one that has recently gone through a period of substantial trade liberalization and we expect that the wage effects of this policy change should show up in the data. Second, most Mexican trade is with countries that are definitely more abundant on skilled labor. Throughout the 1988–2000 period, more than 93% of total Mexican external trade was with the US, Canada, Europe and Japan. This means that if the implications of the Stolper–Samuelson theorem are correct, therefore Mexico is a good candidate for a country where we should expect to observe a reduction in wage inequality as a result of having higher volumes of international trade. Also, if skill-biased technological change is important, therefore we should expect that these two aspects, trade and technology, should be operating in different directions and that the observed wage movements should be a reflection of the relative importance of both aspects. Third, the fact that Mexico signed in 1992 the North American Free Trade Agreement (NAFTA) with much more developed countries such as Canada and the US, suggests that we should expect a deepening of the effects of trade on wage inequality in the post-NAFTA period.6 It is important to stress that we should not expect a change in the role of trade liberalization on wage inequality as a result of NAFTA, since it did not mean a qualitative change in trade policy.7 In order to identify the contribution of technology and trade to the observed pattern of wage inequality in Mexico, we estimated “mandated-wage” equations as suggested by Leamer (1998).8 This methodology, as such, has not been previously applied for developing countries.9 Based on the observed pattern of wage inequality in Mexico, we estimate product–price regressions for the subperiods 1988–1994 and 1994–2000. The motivation for this division is to analyze separately the pre-NAFTA and the post-NAFTA periods. As mentioned before, there are enough reasons to believe that the effect of trade on wage inequality in Mexico must be qualitatively similar before and after NAFTA, but the magnitude of such effect may have increased as a result of the greater economic integration between Mexico and more developed countries such as the United States and Canada. Besides this introduction, Section 2 provides the stylized facts on trade liberalization and wage inequality in Mexico. Section 3 presents a brief survey of the literature on the sources and determinants of wage inequality in Mexico. Section 4 describes the methodology and data that we use in our empirical exercise. Section 5 presents the empirical results. Finally, Section 6 concludes.

Wage inequality in Mexico increased sharply after 1980 and until the mid-1990s, and it has remained almost unchanged since then. The fact that the increase in wage inequality coincided with the period of trade liberalization was puzzling since most people considered Mexico as an unskilled labor abundant country, and the predictions of the conventional trade theory for these type of countries was that a reduction in trade barriers should led to a reduction in the wage gap between skilled and unskilled workers (Stolper–Samuelson theorem). The lack of coherence between theory and reality led many authors in search of an explanation for such a paradoxical result. There were many different approaches and lines of research to address the issue. On the one hand, some authors, based on simple correlations between trade liberalization and wage inequality, suggested that something could be wrong with the theoretical models. Other authors, more creative, developed convoluted explanations to suggest that the theory was right but that Mexico was in reality a skilled labor abundant country. Of course, this line of reasoning could explain now reasonably well why wage inequality in Mexico increased in the aftermath of trade liberalization. However, the assumption that Mexico is a skilled-labor abundant country is difficult to sustain and the story has problems in explaining the recent stability in the wage gap in Mexico. Other authors, more cautious, suggested that there could be something else going on. In particular, several authors suggested the possibility of a skill-biased technological change or a generalized increase in the demand of skilled labor in Mexico. Indeed, several authors found direct and/or indirect evidence in favor of the hypothesis that technological change could be playing an important role in explaining the observed trends in wage inequality in Mexico. Despite this evidence, there were still doubts about the validity of the predictions of the theoretical models, as well as of the relative importance of trade and technological factors in explaining the observed pattern of wage inequality in Mexico. In this paper, we have applied the “mandated” wage approach suggested by Leamer (1998) to separate out the effects of trade and technology in wage inequality in Mexico before and after NAFTA. Our results show that, as suspected, technology was responsible for the sharp increase in wage inequality in Mexico in the pre-NAFTA period. In that sense, our results are consistent with previous findings by Cragg and Epelbaum (1996), Cañonero and Werner (2002), and Meza, 1999 and Meza, 2003. More importantly, however, is that our results show that the effect of trade liberalization in the pre-NAFTA period was exactly in the direction predicted by the Stolper–Samuelson theorem under the assumption that Mexico is an unskilled labor abundant country (as surely it is, at least compared to its main trade partners). That is, in absence of technological change, trade liberalization would have led to a reduction in the wage gap in Mexico in both periods. In the first period, however, the effects of technological change on the wage gap more than compensated the trade liberalization effects, therefore leading to the observed increase in wage inequality. In the post-NAFTA period, the effect of trade liberalization on the wage gap was almost zero, but technological change again pressed for an increase in the wage gap. In this case, however, the magnitude of the increase in the wage gap mandated by the technological change clearly exceeded the observed increase in the wage gap in Mexico. This is an issue that deserves to be explored further. In summary, our results for Mexico show strong support for the predictions of the Stolper–Samuelson theorem in the pre-NAFTA period, and also for the hypothesis that there has been a generalized technological change that has pressed for an increase in the returns to skills. These two effects work in opposite directions in developing countries and the observed pattern of wage inequality will depend on the relative magnitude of both effects.